Mitochondria in the Phloem of Cucurbita

The mitochondria of the phloem-parenchyma cells, the companion cells, and the immature, still nucleate sieve elements of Cucurbita maxima Duchesne have the usual structure of plant mitochondria. They have double outer membranes, tubular inner membranes derived from the inner layer of the outer membrane, and a stainable matrix. 2. In differentiating sieve elements the mitochondria show a dislocation and disorganization of the inner membranes and a lightening of the matrix. The outer membrane is possibly changed also, since its doubleness is rarely discernible. Thus, the mitochondria of mature sieve elements appear to be structurally modified; they resemble mitochondria described in the literature as more or less degenerated.